This invention relates to block copolymers of an xcex1-olefin and a second olefin. The block copolymers are not highly isotactic, but contain isotactic sequences and have a narrow molecular weight distribution. Blends of these block copolymers are disclosed.
Copolymers of an xcex1-olefin and a second olefin are known and are characterized as being random or block, by their molecular weight distribution, and by the stereoregularity of the monomer units. By xe2x80x9cstereoregularity,xe2x80x9d we mean whether the xcex1-olefin recurring units are present in the isotactic, syndiotactic or atactic configuration. These features affect copolymer processability and physical properties. Dependent upon the end use application, different properties are desirable.
Comonomer content and comonomer distribution within the polymer chain also affect copolymer properties. R. Kravchenko and R. Waymouth, Macromolecules 31 (1998) 1, studied arylindene zirconocenes as catalysts for ethylene-propylene copolymerizations. They report random or slightly blocky incorporation of the comonomers (monomer reactivity ratio product, r1r2,=1.0xe2x88x921.9) with the unbridged catalysts and alternating distribution with the bridged catalyst studied. They show a table of eighteen other catalysts previously studied in the literature. None of the thirteen metallocene catalysts gave block copolymers (r1r2 varied from as low as 0.14 to as high as 1.5). Of the Ziegler-Nafta catalysts, heterogeneous titanium catalysts gave block copolymers, but these have a broad molecular weight distribution. None of the polymers had both r1r2 greater than 2.0 and narrow molecular weight distribution.
M. Galimberti et al, Macromolecules 32 (1999) 7968, reported some ethylene-propylene block copolymers but these were completely isotactic (isotacticity index=1.0). U.S. Pat. No. 6,111,046 provides copolymers of ethylene and propylene such that the propylene sequences have an atactic structure and the copolymer is substantially amorphous. U.S. Pat. No. 5,700,896 provides a copolymer with long isotactic sequences but as a random copolymer.
U.S. Pat. No. 6,232,260 discloses the use of transition metal catalysts based upon indenoindolyl ligands. Although it is mentioned that combinations of olefins can be used, all of the examples are ethylene polymerizations or copolymerizations of ethylene with 1-butene. There is no indication that block copolymers could be formed nor is there any indication of stereochemical control.
Pending Application Ser. No. 09/859,332, filed May 17, 2001, now U.S. Pat. No. 6,541,583, discloses a process for the polymerization of propylene in the presence of a Group 3-5 transition metal catalyst that has two non-bridged indenoindolyl ligands wherein the resulting polypropylene has isotactic and atactic stereoblock sequences. No copolymers were prepared and there is no indication given that the process would be suitable for copolymerization.
Generally, copolymers that are highly isotactic (isotacticity index  greater than 0.90) are substantially crystalline. While crystallinity increases stiffness, it often decreases the elastic properties of the polymer. Conversely, copolymers that have low tacticity (isotacticity index  less than 0.40) are usually soft and flexible but will have lower strength and may have a tacky feel. Copolymers having intermediate tacticity would retain some of the stiffness and strength of highly isotactic copolymers, but would have enhanced flexibility and a low degree of tackiness.
xe2x80x9cBlockyxe2x80x9d copolymers, i.e., ones that have r1r2 values greater than 2.0, have the potential to be highly compatible with a wide range of other polymers, e.g., polyethylenes, polypropylenes, elastomeric polyolefins, and the like. Moreover, blocky copolymers can also have enhanced thermal properties.
Copolymers with narrow molecular weight distribution (Mw/Mn) are desirable because they often have improved strength and mechanical properties compared with polymers having broader Mw/Mn values.
Despite the considerable work done in this area, only copolymers with a maximum of two of the desired features have been available. A copolymer is needed with all three features, namely a blocky copolymer, having a narrow molecular weight distribution and stereoregularity that is not highly isotactic but contains relatively long isotactic sequences. Copolymers with all three features should have excellent elastomeric and thermoplastic-elastomeric properties (high tensile strength, high elongation, good elastic recovery) and excellent compatibility with many olefin polymers.
The invention is a block copolymer of an xcex1-olefin and a second olefin. The block copolymer has an isotacticity index of 0.40 to 0.90 and a molecular weight distribution (Mw/Mn) less than 6.0. In addition, the copolymer has substantial blockiness; the product of the reactivity ratios of the olefin monomers (r1r2) is greater than 2.0. Copolymers of the invention have excellent elastomeric and thermoplastic-elastomeric properties and are compatible with many olefin polymers.
Also provided are a copolymerization process and blends of the polyolefin block copolymer with a second polymer. The copolymerization process is done in the presence of an activator and a Group 3-5 transition metal catalyst that has two non-bridged indenoindolyl ligands.
Suitable xcex1-olefins for the copolymerization are C3-C20 xcex1-olefins such as propylene, 1-butene, 1-hexene and 1-octene. Preferred xcex1-olefins are propylene, 1-butene, 1-hexene and 1-octene. Particularly preferred is propylene. The second olefin is different from the first. Suitable second olefins are C2-C20 xcex1-olefins, such as ethylene, propylene, 1-butene, 1-hexene, 1-octene. Preferred second olefins are ethylene, propylene, 1-butene, 1-hexene and 1-octene. Particularly preferred is ethylene. A preferred combination of an xcex1-olefin and a second olefin is propylene and ethylene. A third olefin may be used. Suitable third olefins are C2-C20 xcex1-olefins, such as ethylene, propylene, 1-butene, 1-hexene, 1-octene and non-conjugated dienes such as 1,5-hexadiene and 2,5-norbornylene. Preferably, the block copolymer comprises more than 60 mole % propylene units and more preferably more than 80 mole % propylene units.
The tacticity of a polymer or copolymer affects its properties. The term xe2x80x9ctacticityxe2x80x9d refers to the stereochemical configuration of the polymer. For example, adjacent monomer units can have either like or opposite configuration. If all monomer units have like configuration, the polymer is xe2x80x9cisotactic.xe2x80x9d If adjacent monomer units have opposite configuration and this alternating configuration continues along the entire polymer chain, the polymer is xe2x80x9csyndiotactic.xe2x80x9d If the configuration of monomer units is random, the polymer is xe2x80x9catactic.xe2x80x9d When two contiguous monomer units, a xe2x80x9cdiad,xe2x80x9d have the same configuration, the diad is called isotactic or xe2x80x9cmesoxe2x80x9d (m). When the monomer units have opposite configuration, the diad is called xe2x80x9cracemicxe2x80x9d (r). For three adjacent monomer units, a xe2x80x9ctriad,xe2x80x9d there are three possibilities. If the three adjacent monomer units have the same configuration, the triad is designated mm. An rr triad has the middle monomer unit having an opposite configuration from either neighbor. If two adjacent monomer units have the same configuration and it is different from the third monomer, the triad is designated as having mr tacticity. The configuration can be determined by 13C nuclear magnetic resonance spectroscopy as described in Macromolecules 6 (1973) 925 and references cited therein, and in PCT Int. Appl. WO 00/01745. For more information on polymer stereochemistry, see G. Odian, Principles of Polymerization, 2nd edition (1981), pages 568-580.
The configuration of the monomer units affects polymer properties. For example, highly isotactic polypropylene readily forms a crystalline structure and has excellent chemical and heat resistance. Unlike isotactic polypropylene, atactic polypropylene is amorphous. It has less chemical and heat resistance than isotactic polypropylene. It is mainly used in adhesives.
To quantify the tacticity of a polymer, we calculate an isotacticity index from the configuration of the triads. By xe2x80x9cisotacticity indexxe2x80x9d we mean the quantity of triads having the same configuration divided by the total of all the triads. Therefore, the isotacticity index=mm/[mm+mr+rr]. A completely isotactic copolymer would have an isotacticity index of 1.0. When the isotacticity index is greater than 0.90, the copolymer is highly isotactic. A completely atactic copolymer would have an isotacticity index of 0.25. Copolymers of the invention are not highly isotactic, but contain relatively long isotactic sequences. Blocks of atactic stereosequences may also be present. The copolymers are characterized by having an isotacticity index of 0.40 to 0.90, preferably 0.45 to 0.80.
The copolymer has a narrow molecular weight distribution. The molecular weight distribution can be measured by gel permeation chromatography and is the ratio of the weight average (Mw) and number average (Mn) molecular weights. By a narrow molecular weight distribution, we mean Mw/Mn is less than 6.0, preferably less than 4.0. The molecular weight distribution affects polymer properties such as toughness and processability.
The reactivity of the two olefins affects their distribution within the polymer chain. The monomer reactivity ratio product can be determined by 13C nuclear magnetic resonance spectroscopy as described in Macromolecules15 (1982) 1150. For example, with an ethylene-propylene copolymer, the analysis shows diads corresponding to PP, EE and PE sequences. The monomer reactivity ratio product can be calculated from the diads; r1r2=EE(PP/(PE/2)2). When the comonomer sequence distribution is random, r1r2 is about 1.0. An alternating comonomer distribution r1r2 less than 1.0 and a copolymer with blocks of each comonomer has r1r2 greater than 1.0. The greater r1r2, the longer the block sequences. The copolymer of the invention is a block copolymer and r1r2 is greater than 2.0, preferably greater than 2.5.
The block copolymers can be prepared by copolymerizing an xcex1-olefin with a second olefin in the presence of an activator and a Group 3-5 transition metal catalyst. The preferred catalyst has two indenoindolyl ligands which derive from an indenoindole compound. By xe2x80x9cindenoindole compound,xe2x80x9d we mean an organic compound that has both indole and indene rings. The five-membered rings from each are fused, i.e., they share two carbon atoms. The indenoindolyl ligands are not bridged to each other.
The catalyst preferably has the general structure 
where M is a Group 3-5 transition metal. Preferably, M is zirconium. The indenoindolyl ligands, L1 and L2, are xcfx80-bonded to M. L1 and L2 can be the same or different and preferably have the following alternative structures: 
R1 is preferably selected from the group consisting of alkyl, aryl, aralkyl, and silyl groups. Examples are methyl, t-butyl, phenyl, and trimethylsilyl groups. R2 through R10 are the same or different and are preferably selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, silyl, halogen, alkoxy, aryloxy, siloxy, thioether, nitro, amino groups, and the like.
The catalyst has two other ligands, X1 and X2, which can be the same or different. They are preferably selected from the group consisting of halogen, alkoxy, aryloxy, siloxy, dialkylamino, diarylamino, and hydrocarbyl groups. Labile ligands such as halogen are particularly preferred.
Examples of suitable catalysts include bis-(2-chloro-5-phenyl-5,10-dihydroindeno[1,2-b]indolyl)zirconium dichloride (Structure I), bis-(5-phenyl-5,10-dihydroindeno[1,2-b]indolyl)zirconium dichloride (Structure II), bis-(5,8-dimethyl-5,10-dihydroindeno[1,2-b]indolyl)zirconium dichloride (Structure III), and bis-(5-trimethylsilyl-8-methyl-5,10-dihydroindeno[1,2-b]indolyl)zirconium dichloride (Structure IV). A more preferred catalyst is bis-(2-chloro-5-phenyl-5,10-dihydroindeno[1,2-b]indolyl)zirconium dichloride (Structure I). 
The catalysts can be prepared by any known method. U.S. Pat. No. 6,232,260, the teachings of which are incorporated herein by reference, teaches in great detail how to prepare indenoindole-based catalysts. For instance, Catalyst III can be made according to the following scheme: 
The catalysts are activated. Suitable activators include alumoxanes, alkyl aluminums, alkyl aluminum halides, anionic compounds of boron or aluminum, trialkylboron and triarylboron compounds. Examples include methyl alumoxane (MAO), polymeric MAO (PMAO), ethyl alumoxane, diisobutyl alumoxane, triethylaluminum, diethyl aluminum chloride, trimethylaluminum, triisobutyl aluminum, lithium tetrakis(pentafluorophenyl)borate, lithium tetrakis(pentafluorophenyl)aluminate, dimethylanilinium tetrakis(pentafluorophenyl)borate, trityl tetrakis(pentafluorophenyl)borate, tris(pentafluorophenyl)borane, triphenylborane, tri-n-octylborane, the like, and mixtures thereof.
Selection of activator depends on many factors including the catalyst used and the desired copolymer properties. For instance, in the copolymerization of propylene with ethylene, when bis(2-chloro-5-phenyl-5,10-dihydroindeno[1,2-b]indolyl)zirconium dichloride is used as a catalyst and MAO as an activator, the copolymer produced has higher isotacticity index and longer block sequences than a copolymer prepared while using a combination of triisobutylaluminum and trityl tetrakis(pentafluoro-phenyl)borate as activator.
Optionally, the catalyst is immobilized on a support. The support is preferably a porous material such as inorganic oxides and chlorides, and organic polymer resins. Preferred inorganic oxides include oxides of Group 2, 3, 4, 5, 13, or 14 elements. Preferred supports include silica, alumina, silica-aluminas, magnesias, titania, zirconia, magnesium chloride, and crosslinked polystyrene.
Many types of polymerization processes can be used. The process can be practiced in the gas phase, bulk, solution, or slurry. The polymerization can be performed over a wide temperature range. Preferably, the temperature is within the range of about 0xc2x0 C. to about 150xc2x0 C. A more preferred range is from about 25xc2x0 C. to about 100xc2x0 C.
The unique structure of these copolymers makes them excellent blend components. The relatively long isotactic sequences should enhance compatibility with other polymers and copolymers and give blends with enhanced properties such as improved impact strength, stiffness and clarity. The copolymers can be blended with any of several addition or condensation polymers or copolymers such as polypropylene, polystyrene, polyvinyl alcohol, polyvinyl chloride, EPDM, polyamides or polycarbonate. Preferably, the blend is with polyolefins such polypropylene, polyethylene or LLDPE. Of these, a preferred blend is with polypropylene and a particularly preferred blend is with isotactic polypropylene.